1. Field of the Invention
The present invention relates to a prosthetic leg which is attached to a leg that has been amputated proximal to the knee as a substitute leg and has a hydraulic cylinder for adjusting the bending and extension resistance of a knee joint portion, and which enables walking on stairs, slopes, and level ground without buckling of the knee by employing the movable displacement of a buffer device provided between a lower leg portion and a foot portion below the knee joint portion to lock the knee of the prosthetic leg so that the knee does not buckle when the toe of the prosthetic leg contacts the ground and increase the knee bend resistance of the prosthetic leg when the heel of the prosthetic leg contacts the ground so that the knee bends slowly, and more particularly to a prosthetic leg which enables smooth walking on level ground and down slopes and stairs by allowing the knee to bend without locking the knee when a knee bending operation is performed continuously from a state in which the knee is extended while switching from heel grounding to toe grounding during walking.
2. Description of the Related Art
Japanese Patent Application Publication No. JP-A-H11-19105, Japanese Patent Application Publication No. JP-A-2001-218778, and so on, for example, are known as prosthetic legs that are attached to an amputated leg proximal to the knee as a substitute leg and provided with a pneumatic cylinder or a hydraulic cylinder used to adjust the bending/extension resistance of a knee joint portion.
Further, Japanese Patent Application Publication No. JP-A-2005-87347 has been filed as a prosthetic leg which enables walking on stairs, slopes, and level ground without buckling of the knee by controlling bending and extension resistance in the knee of the prosthetic leg, during use, without detecting muscle contraction in the stump portion of the amputated leg, to lock the knee of the prosthetic leg so that the knee does not buckle when the toe of the prosthetic leg contacts the ground and increase the knee bend resistance of the prosthetic leg when the heel of the prosthetic leg contacts the ground so that the knee bends slowly.
In the invention of Japanese Patent Application Publication No. JP-A-2005-87347, walking on stairs, slopes, and level ground without buckling of the knee is made possible by controlling the bending and extension resistance in the knee of the prosthetic leg during use, without detecting muscle contraction in the stump portion of the amputated leg, to lock the knee of the prosthetic leg so that the knee does not buckle when the toe of the prosthetic leg contacts the ground and increase the knee bend resistance of the prosthetic leg when the heel of the prosthetic leg contacts the ground so that the knee bends slowly.
In the invention of Japanese Patent Application Publication No. JP-A-2005-87347, a toe grounding lock valve 76 and a heel grounding lock valve are disposed independently of each other, leading to a corresponding increase in the number of components, an increase in the amount of required space, and a corresponding increase in the structural complexity of the narrow hydraulic cylinder. Moreover, since the two valves are operated independently, a malfunction in which both the toe grounding lock valve and the heel grounding lock valve enter an open state or both valves enter a closed state may occur.
Further, in the invention of Japanese Patent Application Publication No. JP-A-2005-87347, during walking on level ground, the knee is not locked when the toes contact the ground with the knee in an extended state and when the knee bends to a small angle between 20 and 30 degrees, for example, but when the knee bends beyond this point, the knee is locked. Once locked, the knee does not bend further, and therefore it may be impossible to move smoothly forward when the toes contact the ground.
(Section A of FIG. 9)
Furthermore, when the heel of the prosthetic leg contacts the ground while walking down a slope or stairs, the knee bend resistance is increased so that the knee bends slowly, but when heel grounding switches to toe grounding knee bending is locked, preventing smooth walking.
As a preventative measure, locking may be prevented until the knee bends to 40 or 50 degrees, but in so doing, locking is not performed until the knee bends to 40 or 50 degrees even when walking upstairs, and as a result, it becomes difficult to walk upstairs.